Discrepancy between {R16,R26} & {etax,etaxp} & R56?

[Zamank]

HI All,

For the given lattice (simple accelerating section to chicane) the data from the R-matrix output file does not match well with the twiss output file:

1. etax does not equal R16

2. etaxp does not equal R26

3. The R56 values throughout the chicane at the end (the only source of R56 and R16) of the linac do not allign with that of my own calculations (I used the matrix method); they seem a bit smaller than they should be.

Any ideas?

Thanks!

[michael_borland]

Yes, that's because the definition of etax is in terms of the "local" energy deviation, not the energy deviation at the start of the beamline. They are different when you have acceleration. By default and for a linear system, etax should correspond to Sigma_16/sqrt{Sigma_66} where sqrt{Sigma_66} is the fractional energy spread at the location of observation. R16 in contrast is a transport matrix coefficient from the beginning of the beamline.

If you want them to match, set local_dispersion=0 in the &twiss_output command.

--Michael